Caching is the process of storing information in a readily accessible format for later use. Normally, every time you access a web page, the server has to go out and fetch all of the components of a web page, assemble them, and then display the page to you. By caching the web page, the server can avoid most of the process of assembling pages and serve up the stored (cache) copy instead. Think of it like a squirrel gathering nuts through the summer months for use during the winter. Their stockpile allows them a quick and reliable means of getting to the food they need.
One thing to keep in mind when using caching is that while editing your site, there may be times that the cache does not recognize it needs to refresh the stored version of your web page. If this happens, you may need to clear your cache. This process varies depending on which caching plugin you are using but for Sparked Hosting customers, they should be using LiteSpeed Cache (assuming they are using WordPress).